In traction vehicles with one or more trailers, special stipulations as regards the brake system of the trailer have to be adhered to, particularly when the trailer has hydraulic brake systems. The stipulations and directives for hydraulic trailer brake systems are different from state to state, and because of this the brake systems have to be designed so as to be as variably adjustable as possible, in order to satisfy the various requirements and so that they can be used as universally as possible. Particularly where ensuring a maximum trailer brake pressure is concerned, different standards are applied in Europe. In this case, in most European countries, the maximum trailer brake pressure under the full braking of the traction vehicle must lie between 100 and 150 bar. In France, the maximum trailer brake pressure under the full braking of a traction vehicle must lie even between 120 and 150 bar. Furthermore, when the brake of the traction vehicle is not actuated, no brake pressure should prevail on the trailer. In addition, for example in France, a pressure of 100 bar must prevail on the trailer when the traction vehicle is braked with a deceleration of 25% to 35%. This gives rise to some fundamental problems which are listed below: a non-loaded trailer is braked to a greater extent than a loaded trailer if the brake pressure is the same. Overbraking or underbraking of a trailer and consequently a jackknifing of the entire tractor-trailer may therefore take place. A non-loaded traction vehicle is braked to a greater extent than a loaded traction vehicle if the brake pressure is the same. Here, too, overbraking or underbraking of the trailer and consequently a jackknifing of the entire tractor-trailer may therefore take place. With the brake pressure being the same, large tire diameters generate a lower deceleration force than small tire diameters. This also applies to new and worn tires. In view of these problems, it is difficult to find a correct coordination of the hydraulic trailer brake valve for an entire tractor-trailer.
In the prior art, matching valves, as they may be referred to, which limit the maximum brake pressure on the trailer, are known. Issue No. 8, 2005, pages 54 and 55 of the specialist journal “PROFI” discloses, for example, a hydraulic arrangement for a brake system of the company Paul Forrer AG, in which a variable brake pressure for the trailer can be set via a load-matching valve in the brake line of the trailer, so that the braking behavior can be matched to the different loading states of the trailer. The disadvantage, here, is that the setting of the load-holding valve has to take place manually outside a cab of the traction vehicle. Moreover, this solution entails considerable power losses, since a brake pressure already generated in the brake line is subsequently limited and the remaining brake-pressure excess is therefore squandered.
The object on which the invention is based is seen in specifying a hydraulic arrangement of the type mentioned in the introduction, by means of which the abovementioned problems are overcome.